Population diversity and resilience | Natural selection | AP Biology | Khan Academy

So let's imagine that each of these little circles here represent a member of a population of bugs. We have two different populations of bugs. You could view this as population 1 on the left side of this orange line and population 2 on the right side of this orange line.

These bugs, we're going to think about just one trait: their color, because it's easy to visualize. Let's say that their color generally helps them camouflage from predators. So this kind of cloudy white and black and green layer, that's maybe the environment that they're in, where you might find them—maybe it's the surface of a moss-covered tree or something like that.

These are two separate populations of maybe a related species or maybe the same species, but they're two different populations that are not intermixing. Now, the first question is which of these populations has more genetic diversity?

Well, on the left here, we see that they're all the same color. It looks like a pretty useful color; it seems to hide them pretty well, camouflage them pretty well. On the right here, it's clear that there's more different types of colors. Some of them are roughly the same color as what we see on the left-hand side, but some of them are a good bit darker, and some of them are a good bit lighter. So the one on the right, the population on the right, has more diversity.

Now, one could argue that some of these very bright circles or some of these darker circles might be more susceptible to predators, and that actually might be the case. But what we're going to think about in this video is not how many members of the population may be more or less susceptible to predators. What we're going to think about is: does the diversity help us when there might be some type of changes to the environment? Does it make the population as a whole more resilient?

I'm not talking about any individual member of the population. To imagine that, let's consider that there's some type of environmental change. Maybe there's pollution in the area that makes the surfaces that these little bugs have to live on a good bit darker. So maybe the surfaces look like this.

So now what's likely to happen? Well, in this reality, all of the bugs on our left-hand side are now more visible to predators. You can imagine the predators might be able to pick off a lot more of them. Or, in an extreme case, maybe it will finish them off altogether. While on the right, some of the members of the population are easier to pick off, like that one and that one and that one and that one.

While some other members of the population are even more camouflaged than they were before, like that one and that one and that one. And so the population, because of its diversity, yes, a lot of them might die off; they might be picked off by predators. But it looks like there's a subset of the right population that is going to be more likely to survive, and then they can continue to reproduce.

So you won't have the entire population dying off. You could imagine it the other way around: let’s say instead of the environment getting somehow darker, imagine if the environment got somehow lighter—something like that. Well, you see a similar phenomenon. All the ones on the left are now very similarly visible, and maybe the predators could pick them off.

While on the right, some of them have become a lot more visible. In this case, the darker ones are now super visible. The predators might be able to pick them off. Even some of the medium colored ones, but there's a good number of them that now blend in quite well, like that one and that one, and I can't even see them that well—they're blending in so well.

And so, once again, there are certain members of the populations that, because of this more diversity, they are more likely to be able to survive some type of environmental perturbation. Since they are more likely to survive, the entire population's less likely to be killed off. So the population as a whole is more resilient.

I'm not saying that every member of the population is more resilient, but the population as a whole is. So the general takeaway here is that more diversity leads to more environmental resilience, or resilience to changes in the environment. Once again, we're not talking about every individual member of the population being more resilient; we're talking about the population as a whole being able to survive in some way and then keep carrying on.